Multi-channel closed loop controls having several input channels leading to the same or separate closed loop control systems, include circuit means for forming at their output or outputs a combined control signal. The input signals to the closed loop control are, e.g., deviation signals. The term "deviation signals" in this context refers to signals which are formed as a difference signal from a rated signal and an actually measured signal. In such multi-channel closed loop controls it is essential that at any one time only one channel is actually effective while the other channels are in a standby state. This means that only the deviation signal of the presently effective channel is further processed in the closed loop control to form the control signal. The other channels in their standby state are electrically supplied, however, their signals are switched off by a channel switching logic circuit.
A special construction of such a multi-channel analog closed loop control comprises a redundant control device comprising, preferably, two or even more closed loop control channels, all of which should provide substantially the same control signal. Such redundant controls are required where the failure of one control channel would have unacceptable consequences. In order to avoid such consequences, a channel that has become defective is immediately switched over to a second standby channel which now becomes the controlling channel or operating channel.
Closed loop controls of this type may also comprise an integrator section, for example, a proportional integration controller section or a proportional integration differentiation controller section. These integration sections of the standby channel or channels have assumed a positive or negative saturation state because in practice it is not assured that there is a hundred percent conformity among the input channels. As a result, if, in such a case, a standby channel is switched into operation, generally, a disturbing pulse or interfering pulse is generated in the control system due to the signal jump to the saturation value of the newly switched-in or switched-on integrator.